How do you subtract decemals?

Answer 1

Just line up the decimal point and add zeros where you need them:

3.8 - 1.279

becomes

3.800

1.279

--------

5.218-3

becomes

5.218

3.000

-------

From here, proceed as normal (borrowing, etc.) to find the answer.

Note that I've left out the subtraction sign to make sure numbers align.